Preparation of metal powders



June 27, 1961 J. J. GREBE ET AL 2,990,267

PREPARATION OF METAL POWDERS Filed June 26, 1959 are l reducing 09 en/ hydroxide r- *"1 1 Pro fisc/ive L Reac/or furnace 60s ven/ Separa z or 5/09 Me/a/ 1 0 waereame/aflurg/ca/ app/l'ca/fon prOO/uc IN V EN TORS John E M/V/er BY John! Grebe HTTORNEYS United a s Patent o s 2,990,267 PREPARATION OF METAL POWDERS John J. Grebe and John F. Miller, Midland, Mich., as-

signors to The Dow Chemical Company, Midland, Mich., a corporation of Delaware Filed June 26, 1959, Ser. No. 823,155 8 Claims. (Cl. 75-.5)

This invention is concerned with an improved method for preparing finely divided metallic products suitable for use in powder metallurgical applications. It more particularly relates to a method including the production of finely-particulated metal products encased in a brittle, alkali metal silicate, glass-like protective slag, and grinding this glassy mass to 'yield a product in a form suitable for use in powder metallurgical methods. 7

The utilization of finely divided metallic powders, iron in particular, as starting materials for fabrication of structural metallurgical shapes has grown rapidly in recent years and steadily is increasing in commercial importance.- In addition to the old well-known conventional powder metallurgical applications of pressing and sintering, interest has been growing in the proposed use of continuous rolling, extrusion and forging processes for powdered metals. Flame-spraying techniques and methods of fabrication of large masses of sintered powder without pressing also are now under consideration.

Rapid development of such processes up -to an industrially important scale has been slow to date because of the high cost of powder production, particularly that of the basically important iron and ferrous alloy powders.

. silicate glass-like slag can be reclaimed and economically Methods of production of iron powders may be classifiedin the following manner: (1) direct high tempera? ture reduction of oxidic iron compounds mixed with carbonaceous materials either alone or in the presence of limestone, (2) heating an intimate mixture of high carbon iron powder and iron oxide to achieve simultaneous decarburization and deoxidation of the powders, (3) gaseous reduction of oxides (hydrogen reduction of mill scale), (4) electrolytic deposition of finely divided iron from aqueous ferrous salt solution and (5) atomization of metallic iron or ferrous alloys.

The last mentioned process, atomization, has not been limited to iron based materials alone but also has been used to prepare other metals and alloys in powdered form; examples including, zinc, aluminum, magnesium, brass, copper, stainless steels, Stellite, nickel and the like. Still other general methods for preparation of powdered metals include hydride reduction, chemical distintegration and hydrometallurgical processes.

All of these methods not onlyare expensive means for producingmetal powders, but in addition all suffer from one or more of the following disadvantages: (1) need for precise control of reactant purity, composition and mix ratios, (2.) need for accurate control of reaction temperatures, times, pressures and the like, (3) necessary high quality starting materials not readily available and ('4) resulting powders suffer from inclusion of oxides and other detrimental impurities.

The method of the present invention has overcome the disadvantages of the presently used methods of metal powder preparation and has" as its principal advantage and object the preparation of low sulfur and lowphosphorous containing metal powders at a much lowermost than heretofore realized. A further object and advantage of the present invention is that low quality readilyavailableores can .be utilized as starting products. Another object and advantage of the invention is that metal powders are produced 'directly from the ores or concentrates. Another ,object and advantage ofthe method of this invention is that the co'produceialkali metal converted into useful, commercially important glasses.

Still other objects and advantages will be recognized by one skilled in the art from the description of the invention which follows as well as from the How diagram which illustrates a typical embodiment of the invention. The combination of steps as practiced in the method of this invention comprises in general first mixing comminuted metal ores and silicate slag fluxing agents with finely divided carbonaceous material or other reducing agents and alkali metal hydroxide, using suflicient molar,

proportions of the ore and reducing agent to insure substantially complete reduction of the metal to the metallic state and quantities of alkali metal hydroxide and silicate fluxing agent to insure formation of a continuous, fused glass-like slag. This mixture then is heated at temperatures from about 450 centigrade to about 1225 centigrade,-

for a time sufficient to achieve simultaneous reduction of the ore and production of the alkali metal silicate slag. The resulting thermoplastic mass, comprised of divided metallic products encased in a plastic glass-like slag is cooled and thereby entraps the metal particles in a brittle protective coating. The product is then ground to substantially free therefrom metallic products in a form suitable for use directly in existing conventional or suggested powder metallurgical applications.

Particulated metals which can be produced according to the invention are those having a standard electrode potential between about 1.2 and about minus 0.85; e.g.' manganese, tellurium, zinc, chromium, gadolinium, iron, cadmium, indium, thallium, cobalt, nickel, tin, lead, an timony, bismuth, arsenic, copper, silver and the like. Oxides or sulfides of the metals are the preferred oxidized forms of the metals to use as starting materials although these need not be pure, but can be in the form of the naturallg. occurring ores such as chromite, cobaltite,"

stibnite, arsenopyrite, manganese ore, pentlandite and the like.

Many of the ores, as mined, advantageously will contain varying amounts of silica or other siliceous material such as complex silicates and the like. However, in many cases these silicon containing, glass forming, fiuxing materials are not present or are present in extremely small amounts. If these are not present in sufiicient quantities for production of the glass-like slag, excess silicon dioxide in the form of sand or powdered quartz is added to the mix. Production of the slag itself results from reaction of silicon dioxide and the silicate glass forming fluxing agents present, with the alkali metal hydroxide used in the mix. Potassium-, sodiumand lithium hydroxide all have been found to be suitable for this ap-' plication although sodium hydroxide is preferred. The alkali metal hydroxide is used in any of a number of forms including substantially dry flake, paste, or as an aqueous solution.

The reducing agent normally used in the process is carbon or a material having a high free carbon content. Soft coal and lignite, both of which are plentiful and inexpensive have been found to work very satisfactorily as reducing agents in the method of the invention. However, other reductants which can be employed include metals such as sodium, calcium, potassium, lithium, mag-' the temperature employed. For example, iron oxide can be reduced to metallic iron by reaction at about 1225 Patented June 27, 1961v C. forabout 25 minutes while a reaction time of about i 18.0 minutes is required at temperatures of about 900 C. For the different metals, it will be recognized that both reaction times and temperatures are dependent on the properties of the individual metals. The elements whose standard electrode potentials approach more closely those of the noble metals can be reduced with considerably greater easelower temperatures and reaction times-than those elements near the upper temperature limits of application of the invention, namely manganese, chromium and the like.

Illustrative of an embodiment of this invention is a method for the production of finely divided iron encased in glass and the subsequent separation of the metal therefrom as shown in the flow diagram. The reaction mixture is prepared by mixing one of the comminuted iron containing ores (which can include ores ranging in iron contents from that of the high quality hematites [60-65 percent iron] to the lowest grade taconites [15-25 percent iron]), either in the presence or absence of excess silica, with a finely divided carbonaceous material and an alkali metal hydroxide. The preferred operating compositions of the reaction mixture preferably fall within the range of 0.05 to 3.0 moles of silicon dioxide, 1.0.to 3.0 moles of carbonaceous material and 0.3 to 4.0 moles of the alkali metal hydroxide per mole of the iron oxide content of the ore although effective conversion of the ores into metallic iron can be obtained even though the reaction is run using compositions outside this range.

The reaction components described above are mixed thoroughly in a conventional mixer 2, then placed in a melting pot or crucible and transferred to a furnace 3. This furnace conveniently can be either electrically heated and supplied with a protective atmosphere such as nitrogen, helium or argon. Alternatively, the furnace can be gas fired. In the latter case, excess fuel gas along with the combustion product gases provide the mixture with a natural protective atmosphere. As an alternate to this batch type operation, the mix can be fed from the mixer at a continuous, controlled rate onto a moving grate so timed to give the desired reduction and dispersion of the metallic particles in a single pass through the furnace. The reaction mixture is heated within the range of about 900 to about 1225 centigrade for a period from about 30 to about 180 minutes, and, preferably at about ll centigrade for about 30 to 40 minutes. The resulting soft, glass-like mass then is either cooled slowly or rapidly quenched in a shock-chilling tower 4 using an inert gas or liquid quench medium, to yield a dark, non homogeneous, glassy appearing brittle mass ranging in physical appearance from a true solid to a fixed spongelike structure. This mass consists essentially of a mixture of finely divided, low sulfur and low phosphorous iron encased in the slag and may contain additionally varying amounts of larger iron globules and unreacted mix components. Use of a shock-chill rapid quench here has the additional advantage of helping to fracture the glass-like protective covering away from the iron particles and thus simplify the subsequent grinding operation.

Normally, the cooled mass then can be ground to below mesh (U.S. standard sieve) in a pulverizer 5 by any of a number of conventional means, the purpose being to free the metallic iron from its glass-like coating. Methods of grinding may include, for example, use of jaw, pan, roll or hammer crushers, ball, pebble, rod or hammer mills and disk grinders or by micronizing with a gas stream.

After grinding, the material can be transported to a separator 6 to remove the metallic iron products from the slag and other materials present using devices which may employ the principles of magnetic attraction, electromagnetic repulsion, electrostatics, elastic bounce, electrocapacity behavior, gravity and the like.

It is understood that the iron products produced by this reaction technique would not consist of uniformly T 4 & sized and all finely divided particle s. Therefore, classification 7 of these can be carried out, if desired, again in an inert atmosphere, by any one of a number of common means such as screening, gas classification and the like. Those particles of a size suitable for use in powder metallurgical applications can be removed and either be used directly or packaged, stored and shipped as deslred. The oversize particles can be used in normal iron melting and casting operations.

The iron particles obtained by this integrated process are substantially free of glass, and, as produced are of a high quality thus permitting their direct use in powder metallurgical applications. However, the addition or in olusion of a small amount of the glass-like slag itself is not detrimental for a number of applications, since this latter material which softens at relatively low temperatures and pressures can work advantageously as a lubricant in rolling and extruding operations. Furthermore, the intentional retention or addition of a fair percentage of the glassy slag may be desired in other applications such as impact forging, forge extruding, swedging and hammer-welding in order to enclose and retain with glass the fibrous structure and orientations of the metal crystals in the finished products.

The present invention can be illustrated further by the following examples.

Example I Ground taconite ore, 951.9 grams (containing approximately 3 moles Fe O based on 50 percent Fe 0 in. ore and approximately 6 moles Si0 based on 39 percent SiO in ore), 107.8 grams (equivalent to approximately 9 moles of carbon) of ground soft coal and 494 grams (approximately 12 moles) of flake sodium hydroxide were thoroughly mixed and then placed in a graphite crucible. The crucible and contents then were placed in a gas fired furnace at about 1225 centigrade for about 25 minutes. After this time, the mix was cooled in the crucible. The resulting solid, brittle sponge-resembling mass 'was removed from the crucible and ground in a mortar and pestle. The iron particles were separated easily from the ground mix by passing a magnet over the mixture, the metal particles attaching themselves thereto.

Example 11 Ground taconite ore and ground soft coal of the same quantities as used in Example I can be mixed with 670 grams potassium hydroxide (approximately 12 moles) and the resulting mixture treated in the same manner as described for Example I to yield the desired iron product.

Example III Ground taconite ore and ground soft coal of the same quantities as used in Example I can be mixed with 290 grams lithium hydroxide (approximately 12 moles) and the resulting mixtures treated in the same manner as described for Example I to yield the desired iron product.

Example IV Using the same quantities and types of reaction materials as in Example I, the crucible and contents were heated in a gas fired furnace at about 1054 centigrade for about minutes, after which time the mixture was cooled in the crucible. The resulting solid, brittle spongeresembling mass was treated as in Example I and yielded the desired iron product.

Example V With materials and mix composition the same as in Example I, and utilizing the same experimental mixing and handling techniques, heating the mix at about l082 centigrade in a gas fired furnace for about 40 minutes and subsequently cooling, grinding and separating the products yielded finely divided metallic iron.

Example VI With materials and a mix composition thev same. as in arm's;

. a Example-I, andutilizing the same experimental mixing and handlingtechniques, heating the mix at about 900 centigrade in ,a gas fired furnace for about 180 minutes followed by-cooling, grinding and separation can give finely divided metallic iron the same as produced in Example 1.

Example VII Ground hematite ore, 319.4 grams (containing approximately 1.7 'rnoles l ebased on an Fe 0 content of 85 percent in the ore and about 0.16 mole SiO- based on approximately 3 percent SiO in the ore), 24 grams (equivalent to approximately 2 moles of carbon) of ground soft coal and 30 grams of sodium hydroxide (approximately 0.75 mole and added as a 50 percent solution) after being thoroughly mixed can be transferred to a graphite crucible, the mix then be heated in a gas fired furnace at about 1150 centigrade for about 35 minutes, subsequently cooled and ground and finely divided metallic iron separated therefrom.

The iron powder so produced can be compressed into a compact using a die and plunger type press operating from about 40,000 to about 70,000 p.s.i. The resulting formed compact can be sintered at about 1900 Fahrenheit for about 1 hour in the presence of a reducing atmosphere. The sintered compact after cooling can be utilized directly or if desired, be machined using conventional iron working tools and techniques.

In a manner similar to that shown for the foregoing examples, and using the corresponding metal ore, silica, carbonaceous material and alkali hydroxide, manganese can be obtained from its ore by heating for a suflicient period at a temperature of about 1225 centigrade while lead can be produced at a temperature about 450 centigrade.

embodiments of this invention, it is also understood that other oxidized metal compounds can be utilized in this process to produce a wide variety of powdered metals whose standard electrode potentials range from about 1.2 to about minus 0.85 and includes telluiium, zinc, chromium, gadolinium, cadmium, indium, thallium, cobalt, nickel, tin, antimony, bismuth, arsenic, copper, silver and the like. Furthermore, by using mixtures of the oxidized metal compounds, powdered alloys also can be produced directly.

It is also recognized that reducing agents other than the carbonaceous material utilized in the examples above can be successfully employed. These materials can include metals such as potassium, sodium, lithium, silicon, calcium and magnesium, other carbon containing compounds, certain metal salts and hydrides and the like.

Various modifications can be made in the method of the present invention without departing from the spirit or scope thereof and it is understood that we limit ourselves only as defined in the appended claims.

We claim:

1. An improved method for the production of finely divided metals of those metallic elements having a standard electrode potential falling between about 1.2 and about minus 0.85, which comprises: contacting an oxidized form of said metal and a silicate fiuxing agent with an alkali metal hydroxide and a solid carbonaceous reducing agent at temperatures from about 450 to about l225 centigrade for a period of time sufficent to yield the metal in the form of a network of finely divided particles suspended in a continuous, fused glass-like thermoplastic slag, cooling the mixture to entrap the metal particles within a brittle glass-like protective coating, grinding the mass at a low temperature to free the metal particles from this coating and separating the metal particles therefrom, thereby to provide a metal suitable for application in powder metallurgy techniques. Y

2. An improved method for the production of finely divided metallic iron products which comprises: contacting an iron compound with an alkali metal hydroxide, a

. 6 silicate forming fluxing agent and a solid carbonaceous reducing agent at temperatures from about 900 to about 1225" centigrade for about 30 to about 180 minutes to yield the iron in the form of a continuous network of finely divided particles suspended in a glass-like slag, cooling the mixture to entrap the iron particles within a brittle glass-like protective coating, grinding the mass at low temperatures to free the iron particles from this coating, and, separating the metal therefrom.

3. An improved method for the production of finely divided metallic iron products which comprises: contacting an iron ore with an alkali metal hydroxide, a silicate forming fiuxing agent and a solid carbonaceous reducing agent at temperatures from about 900 to about 1225 centigrade for about 30 to about 180 minutes to yield the iron in the form of a continuous network of finely divided particles suspended in a glass-like slag, cooling the mixture to entrap the iron particles within a brittle glass-like protective coating, grinding the mass at low temperature to free the iron from the protective coating, and, separating the metallic iron therefrom.

4. An improved method for the production of finely divided iron products which comprises: contacting an iron ore with suificient silica to make the content at least 0.05 mole, sufficient solid carbonaceous material to make the content at least 1.0 mole and suificient alkali metal hydroxide to make the content at least 0.3 mole per mole of iron oxide present, heating the mixture at about 900 to about 1225 centigrade for about 30 to about 180 minutes in an inert atmosphere, cooling the resulting dispersion of finely divided iron in slag to encase it in a protective glass-like coating, grinding the cooled brittle mass at low temperatures to free the iron from the protective coating, and, separating the metallic iron therefrom.

5. An improved method for the production of finely divided iron products which comprises: contacting an iron ore with 0.05-3.0 moles silicon dioxide, 1.0-3.0 moles solid carbonaceous material and 0.3-4.0 moles a1- kali metal hydroxide per mole of iron oxide present, heating the mixture at about 900 to about 1225 centigrade for about 30 to about 180 minutes in an inert atmosphere, cooling the resulting dispersion of finely divided iron in slag to encase it in a protective glass-like coating, grinding the cooled brittle mass at a low temperature to free the iron from the protective coating, and, separating the metallic iron therefrom.

6. An improved method for the production of finely divided iron products which comprises: contacting an iron ore with sufiicient silica to make the content at least 0.05 mole, sufiicient solid carbonaceous material to make the content at least 1.0 mole and sufficient alkali metal hydroxide to make the content at least 0.3 mole per mole of iron oxide, heating the mixture at about 1150 centigrade for approximately 30 minutes in an inert atmosphere, cooling the resulting dispersion of finely divided iron in slag to encase it in a protective glasslike coating, grinding the cooled brittle mass at a low temperature to free the iron from the protective coating, and, separating the metallic iron therefrom.

7. An improved method for the production of finely divided iron products which comprises: contacting an iron ore with suflicient silica to make the content at least 0.05 mole, sufficient solid carbonaceous material to make the content at least 1.0 mole and sufficient alkali metal hydroxide to make the content at least 0.3 mole per mole of iron oxide, heating the mixture at about 900 to about 1225 centigrade for about 30 to about 180 minutes in an inert atmosphere, rapidly cooling in an inert gas or liquid to shock quench the mass to aid in fracturing the brittle glass cover away from the iron particles, grinding the mass at. a low temperature to complete the removal of the protective coating from the iron, and, separating the metallic iron particles therefrom.

8. An improved method for the production of oxygen free finely divided iron products which comprises: contacting an iron ore with suflicient silica to make the content at least 0.05 mole, suificient solid carbonaceous material to make the content at least 1.0 mole and-sufficient alkali metal hydroxide to make the content at least 0.3 mole per mole of iron oxide, heating the mixture at about 1150 centigrade for about 30 minutes in an inert atmosphere, rapidly cooling in an inert gas or liquid to shock quench the mass to aid in fracturing the brittle glass cover away from the iron particles, grinding the mass at a low temperature to complete the removal'of the protective coating from the iron, and, separating the metallic iron particles therefrom.

8 References Cited in the file of this patent- Hamilton et al.: Transactions AIME, vol. 187, 1950, pages 1275-1282. Published by the American Institute of Mining, Metallurgical and Petroleum Engineers, Inc., New York, N.Y. 

1. AN IMPROVED METHOD FOR THE PRODUCTION OF FINELY DIVIDED METALS OF THOSE METALLIC ELEMENTS HAVING A STANDARD ELECTRODE POTENTIAL FALLING BETWEEN ABOUT 1.2 AND ABOUT MINUS 0.85, WHICH COMPRISES: CONTACTING AN OXIDIZED FORM OF SAID METAL AND A SILICATE FLUXING AGENT WITH AN ALKALI METAL HYDROXIDE AND A SOLID CARBONACEOUS REDUCING AGENT AT TEMPERATURES FROM ABOUT 450 TO ABOUT 1225* CENTIGRADE FOR A PERIOD OF TIME SUFFICIENT TO YIELD THE METAL IN THE FORM OF A NETWORK OF FINELY DIVIDED PARTICLES SUSPENDED IN A CONTINUOUS, FUSED GLASS-LIKE THERMOPLASTIC SLAG, COOLING THE MIXTURE TO ENTRAP THE METAL PARTICLES 